The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An airplane is propelled by one or several propulsion systems comprising a turbojet engine housed in a tubular nacelle. Each propulsion system is attached to the airplane through a pylon generally located under a wing or at the fuselage.
A nacelle generally has a structure comprising an air intake upstream section, upstream from the engine, a middle section intended to surround a fan of the turbojet engine, and a downstream section intended to surround the combustion chamber of the turbojet engine and harboring thrust reversal means.
The air intake section comprises a cowl including an outer wall and an air intake lip, the lip being adapted for allowing optimal capture towards the turbojet engine of the air required for feeding the fan and the internal compressors of the turbojet engine on the one hand, and a fixed shroud which includes an acoustic panel and which is intended to suitably channel the air towards the blades of the fan on the other hand.
The air intake lip is integrated to the outer wall, which allows suppression of any junction means between these members which may be detrimental to the aerodynamic performances of the nacelle, and the cowl is then designated by LFC (for Laminar Forward Cowl).
The cowl is movable relatively to the shroud between a rear operating position, in which the upstream edge of the lip is located in proximity to or in contact with the upstream edge of the shroud, and a front maintenance position, in which said downstream edge of the lip is moved away from the upstream edge of the shroud, notably for allowing access to the turbojet engine.
The interface area between the lip and the shroud generates aerodynamic perturbations due to the presence of shifts and deviations between these elements, inherent to their attachment with each other.
A known solution for improving the aerodynamic continuity of this interface consists of setting into place in this area an element generally called a “flap”. This substantially cylindrical and flexible element is placed against the inner face of the lip and of the shroud. The upstream portion of this element is attached to the lip, while its downstream portion will radially bear against the shroud.
However, the flaps at the prior art are not fully satisfactory. Indeed, it is seen that depending on the relative axial positioning of the lip and of the shroud, there may exist a too large axial deviation between the flap and the shroud, this deviation may typically attain several millimeters. Further, a radial shift of the shroud with respect to the lip may induce a detachment of the downstream extreme portion of the flap. Both of these phenomena are particularly detrimental to the aerodynamics of the nacelle, since they create recessed areas or produce protruding portions in the airflow which perturb the flow of the air upstream from the engine. Now, the shifts between the lip and the shroud are inevitable, notably because the lip is very regularly translated relatively to the shroud for maintenance operations and then for its putting back into the rear operating position.